This invention relates to a numerically controlled machine tool.
Such machines are known to have a control unit comprising a positioning system including programme-controlled means for outputting position demand data to a motor for driving a tool slide of the machine and means for generating position feedback data from a means for continually measuring the position of the slide, means for manually updating the position demand data by small amounts to make it possible to correct errors in the position of the tool, and a programme-controlled facility for outputting miscellaneous function signals for operations ancillary to the tool positioning operations.
Further, it is known to provide such machines with the facility to perform measuring operations on a surface of the workpiece. To this end the machine is provided with means for automatically replacing the tool by a probe adapted to sense said surface and to provide an output of such sensing. Said positioning system is used to move the probe into a sensing relationship with said surface, and the control unit includes a computer for automatically correlating the probe output with data of the positioning system with a view to (a) determining the position of the surface, (b) determining said error, and (c) updating the position demand data.
It is often desirable to provide an automatic measuring facility in machines not originally equipped in this way but there is a difficulty in doing so essentially because it is not readily possible to gain access to the control unit of the machine for the purpose of said correlation, error determining and updating operations.